There's a stupid amount of strategy involved in RTS games if you're any good, and a lot of it is on the tactical engagement level. High level Starcraft play does indeed have flanking and, believe it or not, manipulation of individual units. Flanking, focus fire, targeting your own units in order to utilize splash damage to harm units you cannot detect... there's a lot of thinking on your feet. When it comes right down to it, the most valuable "resource" in a good RTS like Starcraft is attention. I'd go so far as to say what often seperates above average players from great players is the ability to quickly determine if an engagement requires micromanagement or if your time is better spent elsewhere.
Admittedly though, most players never get to that level, since most RTS games do end when a player falls victim to a stumbling block like the classic zerg rush, fall behind in tech or otherwise put themselves in a situation where micromanagement and tactical play can't cover for their mistakes in strategic play. Most battles are indeed won or lost well before battle is joined. Sun Tzu would have loved it.